Welding or bonding connections are used for the non-releasable connection of at least two components or component regions of an individual component. The objective is a permanent connection by means of the materially engaging joining thereof. In welding connections, the base material is initially partially molten by welding heat. The actual connection is formed only as a result of subsequent cooling when the molten phase is left. In principle, consequently, all materials which can be converted into a molten phase can be welded to each other. The material engagement can be brought about with or without a suitable welding filler in accordance with the welding method used.
In order to obtain the necessary welding heat, energy must be supplied from the outer side. In addition to the movement energy which is intended to be applied for this purpose during friction welding, this energy may also be produced, for example, by means of a suitable heat source. However, when metal materials are welded, the electrical resistance thereof can be used to obtain local heating directly as a result of welding current being introduced. Resistance spot welding has become established in particular in the case of thin-walled elements such as, for example, bodywork components. Welding is carried outusing welding tongs engaged around the metal sheets or metal sheet regions intended to be connected. The metal sheets, are locally pressed against each other by electrodes from opposite sides until an electrically conductive contact is produced between the regions to be welded. Subsequently, the welding current flows via the electrodes through the local contact region to form a welded connection.
In addition to the materially engaging connection of component faces by means of welding, purely bonding methods are also used in many cases. The bonding layer present between the component faces produces a non-releasable bonding connection.